The long-term goal of this project is to develop mathematical and physico-chemical models that describe the cellular response to DNA damage at the network and systems biology level. The work involves the tight integration of focused rigorously quantitative experimental studies monitoring the activity of a large number of intracellular protein kinase signaling pathways and correlating their activity with the cellular phenotypes of DNA damage-induced cell cycle arrest and re-entry, apoptosis or senescence using a variety of quantitative mathematical models. These models capture the relevant signaling information, and provide new insights into the underlying biology. Experiments focus on human lymphoma and breast cancer cells with direct translational relevance, and build directly on our prior experimental and modeling work performed during the previous funding period. In lymphoma cells our focus includes t h e connection between DNA damage signaling, cellular response, and transcriptional regulation since our preliminary data suggests that transcriptional changes are likely to be especially important in predicting the response of this tumor type to treatment. In breast cancer cells, we focus on t h e interactions and cross-talk between the EGFR and DNA damage signaling pathways, since our preliminary data suggests that these signals can b e manipulated advantageously to enhance tumor cell killing using agents that are currently in wide clinical use. The computational models that result from this work illuminate which components of the various signaling pathways are most important for the different cellular responses at various times after the genotoxic stress, thereby defining the critical pathways through which cellular signaling information flows. Predictions from the models for both of these tumor types are then explored and tested at a variety of scales, including in vitro cell culture systems, murine xenografts, and mouse cancer models. Guided by t h e models, key nodes in the signaling pathways implicated as being critically important at particular time points after DNA damage will be identified, providing a mechanistic molecular basis underlying the observed cellular phenotype induced by genotoxic stress. The result of these experiments will be a significantly enhanced understanding of the global DNA damage response at the systems level including mechanisms underlying cancer predisposition and therapeutic resistance, and the identification of critical signaling pathways and molecules that should be targets for therapeutic manipulation in cancer treatment.